Watch Timer Operations; Watch Timer Operation; Interval Timer Operation - NEC 78K0 Series User Manual

10.4 Watch Timer Operations

10.4.1 Watch timer operation

The watch timer generates an interrupt request signal (INTWT) at a specific time interval by using the peripheral
hardware clock or subsystem clock.
When bit 0 (WTM0) and bit 1 (WTM1) of the watch timer operation mode register (WTM) are set to 1, the count
operation starts. When these bits are cleared to 0, the 5-bit counter is cleared and the count operation stops.
When the interval timer is simultaneously operated, zero-second start can be achieved only for the watch timer by
clearing WTM1 to 0. In this case, however, the 11-bit prescaler is not cleared. Therefore, an error up to 2
seconds occurs in the first overflow (INTWT) after zero-second start.
The interrupt request is generated at the following time intervals.
WTM3 WTM2 Interrupt Time
Selection
14
0 0 2 /f
W
13
0 1 2 /f
W
5
1 0 2 /f
W
4
1 1 2 /f
W
Remarks 1. f : Watch timer clock frequency (f
W
2. f : Peripheral hardware clock frequency
PRS
3. f : Subsystem clock frequency
SUB

10.4.2 Interval timer operation

The watch timer operates as interval timer which generates interrupt request signals (INTWTI) repeatedly at an
interval of the preset count value.
The interval time can be selected with bits 4 to 6 (WTM4 to WTM6) of the watch timer operation mode register
(WTM).
When bit 0 (WTM0) of the WTM is set to 1, the count operation starts. When this bit is set to 0, the count operation
stops.
WTM6 WTM5 WTM4 Interval Time
0 0 0 2
0 0 1 2
0 1 0 2
0 1 1 2
1 0 0 2
1 0 1 2
1 1 0 2
1 1 1 2
Remarks 1. f : Watch timer clock frequency (f
W
2. f : Peripheral hardware clock frequency
PRS
3. f : Subsystem clock frequency
SUB
CHAPTER 10 WATCH TIMER
Table 10-4. Watch Timer Interrupt Time
When Operated at When Operated at
f = 32.768 kHz f
SUB PRS
(WTM7 = 1) (WTM7 = 0)
0.5 s 1.05 s
0.25 s 0.52 s
µ
977 s 2.05 ms
µ
488 s 1.02 ms
/2
PRS
Table 10-5. Interval Timer Interval Time
When Operated
at f = 32.768
SUB
kHz (WTM7 = 1)
µ
4
/f 488 s
W
µ
5
/f 977 s
W
6
/f 1.95 ms
W
7
/f 3.91 ms
W
8
/f 7.81 ms
W
9
/f 15.6 ms
W
10
/f 31.3 ms
W
11
/f 62.5 ms
W
/2
PRS
Preliminary User's Manual U17260EJ3V1UD
When Operated at
= 2 MHz f = 5 MHz
PRS
(WTM7 = 0)
0.419 s
0.210 s
µ
819 s
µ
410 s
7
or f )
SUB
When Operated When Operated
at f = 2 MHz at f = 5 MHz
PRS PRS
(WTM7 = 0) (WTM7 = 0)
µ
1.02 ms 410 s
µ
2.05 ms 820 s
4.10 ms 1.64 ms
8.20 ms 3.28 ms
16.4 ms 6.55 ms
32.8 ms 13.1 ms
65.5 ms 26.2 ms
131.1 ms 52.4 ms
7
or f )
SUB
9
When Operated at When Operated at
f = 10 MHz f = 20 MHz
PRS PRS
(WTM7 = 0) (WTM7 = 0)
0.210 s 0.105 s
0.105 s 52.5 ms
µ µ
410 s 205 s
µ µ
205 s 102 s
When Operated When Operated
at f = 10 MHz at f = 20 MHz
PRS PRS
(WTM7 = 0) (WTM7 = 0)
µ µ
205 s 102 s
µ µ
410 s 205 s
µ µ
820 s 410 s
µ
1.64 ms 820 s
3.28 ms 1.64 ms
6.55 ms 3.28 ms
13.1 ms 6.55 ms
26.2 ms 13.1 ms
× 1/f
W
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